Re: FileField

• To: Doug Lindholm <lind@xxxxxxxx>
• Subject: Re: FileField
• From: Bill Hibbard <billh@xxxxxxxxxxxxx>
• Date: Fri, 29 Aug 2003 04:21:48 -0500 (CDT)

Hi Doug,

> I'm looking for an efficient way to store data on disk for quick access
> via VisAD. My data look something like:
>
>    time -> ( (x,y,z) -> (a,b,c) )
>
> and I'd like to cache a subset of the time samples for optimal performace.
>
> I assume I want to use FileField (or FileFlatField?) but I'm not sure
> how to proceed.

You can ignore FileField unless you plan to create a new
implementation of Form that manages data caching between
disk and memory.

> I intend to have a "server" with a large amount of data
> available via RemoteDataReferences. I'd populate the server by reading
> in data the usual way then dumping them to files. One big question is
> how should I create those files and read them. Should I use VisAD
> serialized or binary format (via VisADForm) or should I roll my own
> format and maybe use java.nio's memory-mapped IO?

For fastest performance I recommend VisADSerialForm, as long
as your Data objects fit in memory. Note that constructing a
VisADSerialForm is the same as constructing a VisADForm with
the 'boolean allowBinary' argument = false. These save Data
using Java serialization. It wouldn't be hard to write a new
Form that combined Java serialization with java.nio's
memory-mapped IO. Your new Form would have open() and save()
methods that modified the logic of the saveSerial() and
readSerial() methods of VisADForm.java to use java.nio.

> It would help if I understood the difference between a Form (e.g.
> VisADForm) and a FileAccessor.

You can ignore FileAccessor unless you plan to create a new
implementation of Form that explicitly manages the locations
of sub-objects in disk files. If you are using Java
serialization you can ignore FileAccessor and FileField.

Good luck,
Bill

• Follow-Ups:
  • p.s., Re: FileField
    • From: Bill Hibbard

• References:
  • FileField
    • From: Doug Lindholm